Natural gas dehydration and photolysis of methanol

Natural gas dehydration and photolysis of methanol in flow photoreactors based on Xe2 and KrCl exilamps 

Plan of Presentation

  1. Introduction.

1.1 What are exilamps ?

1.2 Opportunities for exilamps in photochemical applications.

1.3 Tasks, solutions within framework of this work. The key reaction.

  1. Solution to problem 1 about methanol decomposition.

2.1 Experimental equipment and research methods. 

2.2 Results of experiment.

2.3 Methods of methanol decomposition. 

2.4 Conclusions on the problem 1

  1. Solution to problem 2 on water vapour conversion.

3.1 Equipment for experiments and hydrocarbon conversion

3.2 The discussion about results

3.3. Design scheme for water removal and hydrocarbon conversion.

3.4 conclusions on the problem 2

  1. Thanks.  
  2. Summary. 

 

                                                                                                  What is exilamp ?         

Exilamps are a subclass of discharge lamps, and their emission results from the decay of excimer and exciplex molecules. Radiation is generated by the spontaneous transition of an excimer molecule from an excited electronic state to the ground state. Excimer and exciplex molecules are short-lived formations that rapidly decompose, usually within a few nanoseconds, releasing their excitation energy in the form of a UV photon.

                                                                       Spectrum Exilamps, used in our experiment     

Spectrum, KrCl Excimer lamp
Spectrum, Xe2 Excimer lamp

                                                                   Excimer lamps in operating modes 

KrCl lamp in operating mode
Xe2 lamp in operating mode

                                                          Research exilamps in photochemical applications 

Advantages exilamps from the point o view of their adaptation: 

  • Greater Energy o photon ( 3.5-10 eV)
  • Relatively narrow emission band ( up to several nm) 
  • Specific radiation power sufficient for research purposes ( up to several MW /CM2)
  • Possibility o scaling the size of emitter.

In addition, due to the relatively weak heating of the flask of the exilamp ( which has received the name – cold lighting) exilamps allow carried out photochemical reactions, selectively exiting chemical bonds, which makes exilamps as a promising source for number of technologies.

                                                                   Tasks solved within the framework of this work.             

Task 1. Reducing the concentration of methanol in water solutions.

Task 2. Removing water from natural gas in the field. 

Key reaction:

Under the influence of short-wave radiation after the absorption of light (hv) at  a wavelength of 172 nm from exilmap, water undergoes photodissociation ( hemolysis),  reaction of water (H2O), forming into a hydroxyl radical (•OH) and a hydrogen atom (H•••) 

H2O + hv—> H2O* → H••• + •OH

With a high quantum yield of 0.42, thereby, toxic organic matter can be mineralized

                                                     Task 1: Removal of methanol from aqueous solutions.  

Methanol continue to be widely used in the petrochemical and gas industries. 

It is known that when methanol enters water, it reduces the content of O2 ( due to methanol oxidation).

Concentrations above 4 mg/dm3 affect the sanitary regime of water bodies. At content of 200 mg/dm3 inhibition is observed. At the same time, biological treatment methods for not allow one to immediately process and dispose of process and wastewater with such an increased content of methanol. 

We were faced with the task of decomposing methanol at high concentrations. Our analysis revealed that exilamps can be used to solve this problem. 

                                                      Experimental equipment and methods of measurement.            

Construction of fotoreaktor based on KrCl – 

(a) and Xe2-exilamp 

(b) based on barrier discharge. 

  1. Helium balloon 2. Pressure gauge. 3. Valve 4. Reactor 5. Fan 6. Exilamp 7. Power supply 
  2. Sample collector 9. Chromatograph  10. Recorder 11. Methanol 12. Cylindrical reaction vessel. 

                                                                                            Materials and Equipment

  1. Methanol solutions of various concentrations (10-350 mg/l), as well as process solution containing ethanol and formaldehyde produced by  – <Fiks> ojsc <TNX3>
  2. Two barrier coaxial krCl exilamps ( length 60 cm, inner tube dia, 40 mm, tube made of quartz glass at 222nm wavelength at not less than 80 % lamp with power of 60 W.
  3. Sample collector.
  4. The composition of the initial and final water-methanol solution and after ultraviolet irradiation was carried out, using the gas chromatographic method on a “Color-500” chromatograph with a flame-ionization detector on quartz column, ( length 3 m, internal dia 3mm, Pogorag T. Error filled with sorbent. The error in determining the concentration of methanol using the gas chromatic method was 2.5 %
  5. Xe2 – exilamp average emission capacity at a wavelength of 172 nm is no less than 2W ( which corresponds to a luminosity of 20 mW/cm2)
  6. Sealed cylindrical reaction vessel 13 diameter 80 mm, in which was placed Exilamp-Xe2.
  7. During irradiation, the solution was bubbled with nitrogen.
  8. Every experiment was repeated not less than 2 times.



                                                                                   Experimental results, KrCl irradiation.

Irradiation of methanol solutions with KrCl-exylampa did not result in a decrease in methanol concentration. 

Therefore, then 0.01 % solution of nitric acid is added to the solutions at a mass ratio. 

V[HN3OH]/V[HNO3]=10  /

1.Within 16 minutes of irradiation, the concentration of methanol in the solution decreases by an order of  ( with 338 mg/d before 14.6 mg/d ), while the concentration of nitric acid decreased by 4 times. 

                                                                         Experimental results, irradiation Xe2- exilamp

At 16 minutes irradiation of process solutions containing methanol, Xe2- ( λ ~172 nm) concentration methanol decreased from 35mg/l and lo 2.6mg / l and 39.2mg/ l

                                                                                              Mechanism of reaction

Primary of reactions: photolysis and nitric acid with the formation of highly reactive radicals

•OH, •H, NO2• and •NO:                                                           

H2O + hv —> H2O*  —> H• + •OH,                                                                                               (1)               

HNO3 + hv —> HNO3*  —> NO2• + •NO + H2O,                                                                (2)

 

Secondary reactions with methanol to form end products

CO2, H2O and NH3.

  • OH + CH3OH –> •CH2 (OH) + H2O                                                                               (3)
  • H + CH3OH –> •CH2 (OH) + H2                                                                                        (4)
  • NO + •CH2 (OH)–>CH2(OH) NO <-> H(OH)C=N(OH)                                       (5)
  • NO + •CH2 (OH)–>CH2(OH) NO <-> H(OH)C=N(OH)                                       (6)

H(OH)C=N(OH) <-> HC(O)NH(OH) <-> O=C-NH+H2O,                                                  (7)

O=C=NH+H2 –>CO2+NH3                                                                                                               (8)

 

The final products of the interaction of formic acid with radicals

•OH are carbon dioxide CO2 and water. 

                                                                                                  Conclusion for task 1 

 1. It has been shown that under the influence of ultraviolet radiation with a wavelength of 𝛌- 172 nm (Xe2-exilamp to  an water-methanol solution in the presence of nitric acid.

        ( mass ratio of methanol/nitrogen content = 10/1 ) methanol concentration water-methanol solution decreased 13 times. )

2. For the first time the possibility of using radiation with the wavelenght of 𝛌- 222 nm (KrCl- exilamp) what reduced the concentration of methanol in the water solution 23 times. 

3. The main product of methanol oxidation is carbon dioxide and water

                                                                Task 2: Removal of water from Natural Gas in the field.   

Removal of water from natural gas and separation of heavy hydrocarbons components in Russia is carried out using low-temperature processes, which are carried out both in the field and in factory conditions. These processes:

  • In energetic sense imperfect;
  • Have bulky design which leads to high capital cost. 

Therefore, the search for new technologies for physical influence on target components in natural gas condensate fields, as well as the development of psyhico-chemical methods or intensifying traditional low-temperature processes is an urgent task. 

                                                              Experimental equipment and method of measurement              

Design of flow photoreaktors based on KrCl and Xe2-barrier discharge exilamps.

 1-natural gas cylinder, 2-pressure gas, 3-valve, 4-gas tube, 5-ventilator, 6-exilamp, 7-power supply, 8-sample collector, 9-chromotograph, 10-recorder, 11, 12-vent tube, 13-cylindrical vessel

                                                                                        Materials and Equipment

  1. Natural gas from the Myldzhinsky gas condensate district of tomsk, provided by jsc Tomsgazprom. Natural Gas under pressure 5-7 MPA reduced through a high pressure reducer ine adjustment valve to atmospheric pressure and falls into the irradiation KrCl-or Xe2-exilamps
  2. The composition of the initial and final water-methanol solution and after ultraviolet irradiation was carried out, using the gas chromatographic method on a “Color-500” chromatograph with a flame-ionization detector on quartz column, ( length 3 m, internal dia 3mm, Pogorag T. Error filled with sorbent. The error in determining the concentration of methanol using the gas chromatic method was 2.5 %
  3. Xe2 – exilamp average emission capacity at a wavelength of 172 nm is no less than 2W ( which corresponds to a luminosity of 20 mW/cm2)
  4. Sealed cylindrical reaction vessel 13 diameter 80 mm, in which was placed Exilamp-Xe2.
  5. During irradiation, the solution was bubbled with nitrogen.
  6. Every experiment was repeated not less than 2 times.

                                                                  Component composition of natural gas, mol %

As can be seen from the component composition of the original natural gas content. Methane is 92.8 % hydrocarbons C2 and above 6.98 % water 0.28 %

                                                                                        The discussion of the results

  1. The components undergo the greatest relative changes C6+ i H2O. This is especially noticeable when using Xe2-exilamp radiation. The C6+ content in this case increases approximately to twofold.  The concentration of water vapour decreases from 0.25 to 0.14 mol. % ( 1.8 times). By absolute concentration. The biggest change is the concentration of water vapour,   Δ[H2O]=0.11%(Δ[C6+]=0.05%).
  2. The mechanism  for the hardening of hydrocarbons is the dimerization of hydrocarbons. The mechanism has been well studied in plasma-chemical reactors with barrier discharges. It occurs in directions with hydroxyl radicals:    
  3. CnH2n+2 + •OH ->  •CnH2n+1 + H2O                                                     (1)
  4. CnH3n+1 + •CmH2m+1 -> C(n+m)H2(n+m+1)                                    (2)
  5. Water removal mechanism. Water removal under by UV radiation. Radiation from natural gas, which includes a large set of organic and inorganic gaseous components, has not been previously studied. 

                                                                         Diagram of the water  removal process

1. Photolysis of water:

H2O + hv —> H2O*  —> H• + •OH,                                                                                                 (3) 

2. Converting the resulting hydroxyl radicals into hydrogen peroxide and H2O:

  • OH + •OH  + M –> H2O + M,                                                                                                 (4a)
  • OH + •OH –> H2O + •O,                                                                                                          (4b)

3. Interaction of oxygen radicals with organic compounds C3-C6 with the formation of organic radicals: 

  • O + CnH2n + 2 → OH + μ- •CnH2n+1,                                                                               (5)
  • OH + CnH2n + 2 → μ- •CnH2n+1+ H2O                                                                          (6)

4. Recombination of hydrocarbon radicals with each other or with hydroxyl radicals. 

  • OH + CnH2n + 1+M –> CnH2n+1OH + M                                                                        (7)
  • CnH2n + 1  •CnH2n+1+M →  μ- C2nH4n + 2+ M                                                         (8)

CnH2n + 1OH +  hv →  CnH2n + 1OH* → CnH2n + 1• + •O                                              (9)

As a result, the synthesis of dimers and alcohols. 

                                                                                             Conclusion on task 2

  1. It has been shown that under the influence of ultraviolet radiation on natural gas, the concentration C6+ doubles. It has been shown that under the influence of ultraviolet radiation from Xe2-exilamp on natural gas, the concentration of water vapor in natural gas decreases by 1.8 times, and when using KrCl- exilamp 1.25 times.
  2. The preliminary results obtained show that the impact of powerful ultraviolet radiation in the above wavelength range on gas condensate deposits leads to an increase in content in gas of heavy components due to directed photochemical processes  dimerization, primary propane and butane.More complex photochemical processes are realized due to the presence of water vapor. 

  3.  According to proven calculations, the main process that lead to a decrease in the water content in gas from natural gas, are photodissociation reaction H2O followed by oxidation of compounds C3-C6. The main products of the oxidation of alkanes are alcohols and aldehydes.

  4. The process of photoirrydation of natural gas in the ultraviolet range can be integrated into the process of low-temperature gas separation to increase yield of heavy hydrocarbons, and for lean gases it is used as a stage for preliminary gas drying. 

Conclusion, after removal of methanol from aqueous solutions. 

 

Methanol continue to be widely used in the petrochemical and gas industries. 

It is known that when methanol enters water, it reduces the content of O2 ( due to methanol oxidation).

Concentrations above 4 mg/dm3 affect the sanitary regime of water bodies. At content of 200 mg/dm3 inhibition is observed. At the same time, biological treatment methods for not allow one to immediately process and dispose of process and wastewater with such an increased content of methanol. 

We were faced with the task of decomposing methanol at high concentrations. Our analysis revealed that exilamps can be used to solve this problem. 







 

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